Reset Values in Subset of Image
Reset the values in a subset of a pixel image.
## S3 replacement method for class 'im' x[i, j, ..., drop=TRUE] <- value
x |
A two-dimensional pixel image.
An object of class |
i |
Object defining the subregion or subset to be replaced.
Either a spatial window (an object of class |
j |
An integer or logical vector serving as the column index
if matrix indexing is being used. Ignored if |
... |
Ignored. |
drop |
Logical value specifying what happens when |
value |
Vector, matrix, factor or pixel image containing the replacement values. Short vectors will be recycled. |
This function changes some of the pixel values in a
pixel image. The image x must be an object of class
"im" representing a pixel image defined inside a
rectangle in two-dimensional space (see im.object).
The subset to be changed is determined by the arguments i,j
according to the following rules (which are checked in this order):
i is a spatial object such as a window,
a pixel image with logical values, or a point pattern; or
i,j are indices for the matrix as.matrix(x); or
i can be converted to a point pattern
by as.ppp(i, W=Window(x)),
and i is not a matrix.
If i is a spatial window (an object of class "owin"),
the values of the image inside this window are changed.
If i is a point pattern (an object of class
"ppp"), then the values of the pixel image at the points of
this pattern are changed.
If i does not satisfy any of the conditions above, then
the algorithm tries to interpret i,j as indices for the matrix
as.matrix(x). Either i or j may be missing or blank.
If none of the conditions above are met, and if i is not
a matrix, then i is converted into a point pattern
by as.ppp(i, W=Window(x)).
Again the values of the pixel image at the points of
this pattern are changed.
If i and j are both missing, as in the call
x[] <- value, then all pixel values in x
are replaced by value:
If drop=TRUE (the default), then
this replacement applies only to pixels whose values are currently defined
(i.e. where the current pixel value is not NA).
If value is a vector, then its length must equal
the number of pixels whose values are currently defined.
If drop=FALSE then the replacement applies to all
pixels inside the rectangle Frame(x).
If value is a vector, then its length
must equal the number of pixels in the entire rectangle.
The image x with the values replaced.
If you have a 2-column matrix containing the x,y coordinates
of point locations, then to prevent this being interpreted as an
array index, you should convert it to a data.frame
or to a point pattern.
Adrian Baddeley Adrian.Baddeley@curtin.edu.au, Rolf Turner r.turner@auckland.ac.nz and Ege Rubak rubak@math.aau.dk.
# make up an image X <- setcov(unit.square()) plot(X) # a rectangular subset W <- owin(c(0,0.5),c(0.2,0.8)) X[W] <- 2 plot(X) # a polygonal subset R <- affine(letterR, diag(c(1,1)/2), c(-2,-0.7)) X[R] <- 3 plot(X) # a point pattern X[cells] <- 10 plot(X) # change pixel value at a specific location X[list(x=0.1,y=0.2)] <- 7 # matrix indexing --- single vector index X[1:2570] <- 10 plot(X) # matrix indexing using double indices X[1:257,1:10] <- 5 plot(X) # matrix indexing using a matrix of indices X[cbind(1:257,1:257)] <- 10 X[cbind(257:1,1:257)] <- 10 plot(X) # Blank indices Y <- as.im(letterR) plot(Y) Y[] <- 42 # replace values only inside the window 'R' plot(Y) Y[drop=FALSE] <- 7 # replace all values in the rectangle plot(Y) Z <- as.im(letterR) Z[] <- raster.x(Z, drop=TRUE) # excludes NA plot(Z) Z[drop=FALSE] <- raster.y(Z, drop=FALSE) # includes NA plot(Z)
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